Method of concentration of ores



H. R. ROBBINS.

METHOD OF CONCENTRATION OF ORES.

APPLICATION FILED OCT. 21, 1919.

1,398,394 Patented Nov. 29, 1921.

3 SHEETS-SHEET H. R. ROBBINS.

METHOD OF CONCENTRATION OF ORES. APPLICATION FILED OCT. 21, 1919.

1 ,39, 39% Patented Nov. 29, 19211.

3 SHEETSSHEET 3.

Invent/ o r:

UNITED STATES PATENT OFF-ICE.

METHOD OF CONCENTRATION 01E OREB.

Specification of Letters Patent.

Patented N 0v. 29, 192-1.

Application filed October 21, 1919. Serial No. 332,345.

To all whom it may concern:

Be it known that I, HALLET RICE Romans, a citizen of the United States,residing at Manchester, in the county of l-lillsborough, State of New Ilampshire, have invented certain new and useful Improvements in Methodsof Concentration of Ores; and I do hereby declare the followin to be afull, clear, and exact description of the invention, such as will enableothers skilled in the art to which it appertains to make and use thesame.

My invention relates particularly to a process for the concentration ofores by the froth flotation process, in which the constituents of oresare separated as a froth formed by the aeration of a liquid pulpconsisting of the finely-ground ore and water, modified by the presenceof a flotation agent, such as finely-divided emulsified or dissolvedoils, or dissolved organic compounds or inorganic salts; but is alsowell adapted for other chemical, physical or metallurgical operationsrequiring eflicient circulation and aeration of liquids or semi-liquids.

Among the objects of my invention are the provision of an apparatus andprocess which will be cheap both to install and to operate; eflicientmechanically and metallurgically; adjustable to the varying conditionsdemanded by ores of differing physical and chemical characteristics; orby substances other than ores; and suited to the economical handling oflarge tonnages; and

which has advantages in these respects over methods and apparatus forthe flotation treatment of ores or for similar purposes known or used atthe present time.

The flotation process is now practised in apparatus consisting ofcomparatively small units, each of which requires individual attentionand adjustment. So far as I am informed this is true of both themechanical agitation method of introducing air and of the method .ofintroducing air through a permeable medium. In the latter method,especially when minerals of high specific gravity are treated, particlesof mineral become embedded in the porous medium thus increasing anyinitial variations in the degree of permeability of different parts ofthe medium and causing an uneven distribution and waste of air. This, inconnection with an uneven and irregular circulation of the pulp in thoseinstances where the pulp is circulated, prevents that maximum contactbetween ore particles and bubbles which formspne of the principalobjects of my invention.

Among the characteristic features of my invention are (1) a positivecirculation of the pulp through the zone of aeration; (2) asubstantially uniform distribution throughout the body of the ore pulpof,a very large number of extremely fine anbubbles; (3) provision forskimming the froth, where this is necessary or important (4) anarrangement such that there is a minimum delay and inconvenience inrestarting, after a sudden and unexpected fallure of the power or airsupply; (5) economy in power required; (6) air, due to increased depthof pulp through whlch the air passes; (7) cheap installation, with aminimum number of moving parts, and no parts moving at high speeds; (8)operation not requiring close and constant attendance; (9) economy oftreatment of large tonnages of low grade ores; and (10) adaptation toeither continuous treatment of ore pulp by flotation, or operation onthe intermittent or charge system. The importance of these advantageswill be ap parent from the following discussion.

1. A positive circulation of the pulp through the zone of aerationshould be proyided, for two principal reasons: First, to insure that allparticles of the ore shall be presented to flotative tendencies as manyM11195. as possible, as the forces causing the flotatlon of minerals areextremelyrsmall, and it has been found absolutely necessary to presentmany of the ore particles to these forces a large number of times inorder to insure this flotation. In an apparatus not provided withpositive circulation, it is inevitable that many particles will not beexposed to flotative forces a sufficient number of times, resulting intheir loss in the tailings, or in the necessity of using additionalunits of the apparatus to save them. If the ore contains a considerableamount of mineral of high specific gravity, or in coarse particles,unless positive circulation is provided, parts of the apparatus willsooner or later become choked with settled mineral.

2. There should be distributed throughout the body of the pulp, asuniformly as possible, a very large number of extremely fine airbubbles,which collect the mineral to be floated and raise it to the surface,where the bubbles form a froth which holds economy 1n a to overflowbefore it breaks to ether with considerable amounts 0 the floatedmineral until it overflows or is skimmed. If the distribution of the airbubbles is not uniform, or if the bubbles aretoo large, violenteruptions of the sur face of the pulp are caused, which break down thefroth, and contaminate it with minerals which it is not desired tofloat.

A principal object of my invention is to cause a uniform distribution ofminute bubbles without incurring the expense of mechanical agitation orthe irregular action incident to the use of porous blankets, and toaccomplish these results in such a way that the necessary apparatus forintroducing air may be removed and replaced for inspection, cleaning andre air without emptying the cell or OthBIWlSB seriously interfering withthe operation of the plant.

3. Provision should be made for skimming the froth in most cases. Inexisting forms of apparatus in common actual commercial use this isfound only, so far as I am aware, in machines using violent mechanicalagitation for beating air, into the ore pulp. In apparatus using directaeration through porous blankets, air-tubes, etc., the froth must beformed ra idly enough own, and no skimmers are commonly used on suchapparatus, nor can they be so used without adding materially to thecomplexity and cost of the apparatus, and interfering with its operatingadjustments. I I have found that a cleaner concentrate and higher ratioof concentration is obtained when the froth is restrained from a freeoverflow, and time given for. a coalescence of the bubbles, whichpermits the dropping out of the froth of mineral and gangue accidentallyand mechanically entangled with it. With some ores containing a smallpercentage of highgrade mineral like chalcocite, a dirty concentrate,containing 40% insoluble may be made, and yet contain 40% copper, and bean acceptable product for the smelter,

and show a high ratio of concentration;

and with such ores the imperfection of existin neumatic flotationapparatus does not f ul y appear. In the case of ores, however,containing large percentages of lowgrade mineral, such as cupriferouspyrite,

other mmeral differing only slightly from the cupriferous pyrite in itsflotative properties, such for example as non-cupriferous pyrite oryrrhotite, then it is necessary to restrain the froth and permit it toclean itself by coalescence of the bubbles, skimming it from theapparatus by mechanical means, otherwise the ratio of concentration willbe found excessively low, so much so in some cases as to make the entirescheme of concentration unadvisable and uneconomical.

4. Myimproved process may be practised with apparatus so arranged thatthe minimum delay and inconvenience in re-starting is caused by a suddenand unexpected failare of the power or air supply. Insubstantlally alltypes of existing apparatus, it is necessary to empty them immediatelysuch a sudden stop age occurs, thus-throwing away all the mineral in theapparatus at the time; or, if not emptied promptly, then they must bedug out with a shovel, or sluiced out with a hose before operations canheresumed, and every such interruption causes a certain period of poormetallurgical results, while the different units of the apparatus arebeing refilled, and smooth and suitable'ope-rating adjustments are beingrestored, which cannot usually be done in less than an hour under themost favorable conditions.

5. The apparatus necessary for my improved process is economical ofpower.

ower is required for two principal purposes in a flotation machine,first, to keep the pulp in circulation, and, second, to comress the airused for forming the collectmg and froth-building bubbles. In all typesof machines employing mechanical agitation, a very high percentage ofthe power used is wasted. In the apparatus employing straight pneumaticflotation, much more air than required for the froth must be used, inorder to cause a sufficient agitation of the pulp to prevent itsexcessive settlement' on the porous blanket during its passage'throughthe apparatus.

6. The apparatus used in the practice of my process is economical ofair, and hence of power required to compress the air used. If the aircan travel upward through six feet of pulp, the bubbles will come incontact with roughly three times as many ore particles as would be thecase with a body of pulp only two feet deep, or in other words the airconsidered as a collecting and separating medium would be used aboutthree times more efficiently in the former case than in the latter. Infew if any forms of existing apparatus is it possible to use a depth ofpulp over the porous blankets of more than two or three feet, owing tothe difficulty in preventing settlement of the heavy ore particles. Airshould not be used for agitation to prevent settlement, nor should moreair be used than is required to form a froth of the proper texture.

7. The necessary apparatus is cheap to install, and contains a minimumpossible number of moving parts, and no parts moving at hi h speeds. Thepartsare, moreover, of simp e construction, readily assembled, andaccessible for inspection and repair.

8. My process is cheaply operated and not dependent for goodmetallurgical results on close and constant attendance.

9. The process is adapted to the economigrade ores, which is equivalentto the state- 'ment that the necessary apparatus may be providedin unitsof large size.

differential separat1ons,'where it gives better results than continuoustreatment, so that any process or apparatus to be of universalapplication must be suited to the use of the intermittent system ifdesired. In no form of existing flotation process or apparatus, so faras I am aware, is it possible to carry on a commercial flotationoperation on the intermittent system.

The nature and advantages of the invention will be further described andillustrated by the accompanying drawings and the following descriptionillustrative of the preferred embodiment thereof and of the preferredconstruction and operation. It should be clearly understood, however,that 1 do not limit myself to the precise form of apparatus shown in thedrawings and described below, but may use other apparatus of differentproportions, and with different details, operating on similar )rinciplesand accomplishing its results in substantially the same manner.

In the accompanying drawings Figure 1 illustrates a preferredconstruction and embodiment of the invention, in central verticalsection;

Fig. 2 is a top view taken on the line 2-2 of Fig. l;

Fig. 3 is a detail view showing the tailings outlet;

Fig. 4: is a horizontal section taken on the line 4.-4 of Fig. 1;

Fig. 5 is an enlarged view illustrating a vpreferred embodiment of theair distributing pipes; and

Fig. 6 is a sectional view taken on the line 66 of Fig. 5.

Fig. 7 is a vertical central sectional View illustrating modified meansfor elevating the pulp..

Referring to the accompanying drawings, and the reference numeralsthereon 1 is an ordinary tank, of approximately cylindrical shape, witha flat bottom,.and of relatively larger size than any containerheretofore used for a flotation separation, in so far as I am aware. Asuitable size would be about 18 feet in diameter, and about 10 feetdeep. The tank may be made of wood staves, steel plate, concrete orother suitable material. This tank 1 is provided With a hollow verticalconduit, 2 open at the bot tom and top, and suspended from a connectingcasting 3 which in turn is fastened to a vertical shaft 4 provided withsuitable bearings 5 and driving mechanism 6 for imparting acomparatively slow rotary movement to the same. To the connectingcasting, .3 are fastened'two distributing launders 7 in the bottom ofwhich are several short pipes or launders 8. To the bottom of the hollowvertical conduit are fastened inclined arms 9 provided with diagonalrabbles l0 and supported by the hinged links 11 to which are attachedthe chains 12. The inclined arms 9 are fastened to the hollow conduit 2by means of hinged connections, about which they are free to rotate. 'Apipe l3 is provided for the introduction of air under pressure withinthe hollow conduit 2 near the bottom of the same.

14, 14; are air mains for conveying air under suitable pressure to themanifolds 15. The air mains are connected to the manifolds through theswivel joints 16 and the swivel pipes '16. Into the manifolds 15 arescrewed, or to them are otherwise suitably connected, the a1r-tubes 16an enlarged desuitable intervals by the bolts 20 and provided with theeye-bolts 21 and lifting chains 22. The entire tube-grates, consistingof the manifolds and air-tubes are supported on the brackets 24 fastenedto the sides of the tank 1. The tube-grates are not fastened to thebrackets 24: but simply rest upon them.

25, 25 are a number, such as four, froth skimmers, consisting of lightsections of sheet metal or other suitable substance, curved as shown,and with a sloping bottom edge. so proportioned that at its lowest pointit is at 01' slightly below the pulplevel, and at its highest point itis about on the same level with the top of the tank 1. The frothskimmers may be supported substantially as shown, from the revolvinglaunders 7 and from the shaft 4 through the chains 26. The action of theskimmers is supplemented by the action of the diagonally arrangeddistributing pipes 8. The inner ends of the skimmers 25 may beadjustable to different positions, to increase the skimming effect, a.g. to positions indicated in dotted lines at 25.

, 27 are hooks, so positioned as not to be interfered with by the frothskimmers, for supporting the ends of the lifting chains 22 attached tothe tube-grates. 28 is a short piece of pipe, open at the end, androtatable about the swivel joint 29 and provided neath the I ofwthe airdischarged from the .pipe 13.

The new feed and circulating pulp, mixed together, pass through therevolving launders '7 and pipes 8 which pass through the bed of froth,and discharge at or slightly beul -level. In this way the pulp isuniform y istributed, over the surface of the contents of the tankbeneath the froth,

and hence without objectionable disturbance of the froth. As the oreparticles in the pulp settle downward, they are exposed to thefloatative action of the fine air bubbles emitted from the air-tubes,and those which are not floated eventually pass down between theair-tubes, and then are moved gradually toward the center of the tank bythe rabbles 10 on the slowly-revolving arms 9. At the center, they aredrawn up into the vertical hollow conduit 2 to replace the pulp forcedupward therein ;by air diischarged from the pipe'13. It is seen that apositive circulation of the entire pulp is insured, regardless of thesize or weight of any individual particles therein.

The air discharged from the air-tubes 16 is brought into the apparatusby the fixed air main 14 and passes through the swivel pipe 16 and themanifold 15 into the airtubes 16 and from them is discharged into thebody of pulp, in the form of extremely fine bubbles, forced through therope 18. The air bubbles travel a longer distance vertically than inexisting forms of apparatus, due to the increased depth of the tank andof the pulp therein, and consequently have more opportunity to pick upfloatable mineral. The bubbles form a froth on the surface'of the pulp,which is not disturbedby the passage of the circulating pulp through thepipes 8. The froth is forced to the edge of the tank by the curvedskimmers and by the diagonally arranged pipes 8 and is propelled by themover the edge into the collecting launder 32 from which .it passes awayfrom the apparatus as the finished product, or to a place of furthertreatment. The form of the Skimmers, as well as the character of thecurve and shape and form of the lower edge, may be varied to lsuitdifferent conditions. In certain cases it is even feasible to dispensewith the froth Skimmers altogether, and permit the froth to overflowfreely.

\Vhen the apparatus is used in a continuous process, there will usuallybe several units in series, and the tailings may be continuouslywithdrawnthrough the pipe 28 discharging into a launder leading to thenext machine, or to waste, as the case may be. The pulp level in thetank is regulated by the position of the end of the pipe 28 and thisposition may be simply and readily adjusted by rotating the ipe 28around the swivel joint 29. In 0l( er to prevent the choking of the pipe28 by particles too heavy to be carried upward b the velocity of thepulp-stream therein, tie small hole 30 is provided through which heavyand coarse particles may pass directly out of the machine. The size ofthis hole is such as to limit its capacity as a discharge orifice tolessthan the product of the apparatus, and in that way it cannot affectthe pulplevel, which Wlll be dependent solely on the vertical positionof the end of the discharge-pipe.

If it is desired to use the apparatus on the, charge or intermittentsystem, the discharge pipe 28 may be dispensed with, or raised to aninoperative position, the tank 1 filled by any convenient means, thecharge being circulated through the zone of aeration provided by the airdischarged through the tubes 16 until the proper separation has beenmade, when the remaining material may be drawn off through thegate-valve 31. In order tocombine the advantages of intermittent andcontinuous operation, an even number of units of the apparatus may beused, and at any given moment half of them would be in process of beingfilled or emptied, and the other half would be under circulation andaeration. The .renoval of the froth would be similar in intermittent orcontinuous operation of the apparatus.

he quantity of air discharged through the end of the pipe 13 should andneed be no more than ust enough to impart the desired upward velocity tothe pulp in the hollow conduit 2 on the principle of the air-lift, wellrecognized as one of the most economical methods for the elevation ofliquids through small differences of elevation. This air is not used toagitate the pulp, nor as a source of collecting and frothformingbubbles, and practically all of it escapes directly into the atmospherefrom the top of the connecting casting 3 as soon as it has fulfilled itssole function of elevating the pulp within the hollow conduit 2. Thequantity of air discharged through the air-tubes 16 should and need beno more than enough to furnish the bubbles to collect the mineral andform the froth. No agitation is required, as choking of the 'ap aratusby settled mineral is prevented by tlie rabb cs which keep everything inconstant motion toward the entranceof the vertical conduit. The functionof the rabbles 10 is solely to move the settled pulp slowly toward thecenter of the apparatus, and the move far too slowly to agitate? it inthe s ightest failure of the power supply, and consequent stoppage ofthe revolving arms 9 the pulp will immediately begin to settle on thebottom of the tank, and if the delay in re-starting should beconsiderable, and if the apparatus is not emptied, the tube-grates mayadvantageousl be lifted all or part way out ofjthe tan This may beaccomplished without delay or difficulty of any kind, and withoutdisconnecting any pipes, by simply turning the vertical shaft until thelaunders 7 are directly over the clear space between the twotube-grates, then attaching the ends of the lifting chains 22 which aremaintained within easy reach, on'the hooks 27, to blocks convenientlysuspended from the roof overhead, and hoisting the tube-grates as highas desired, the air connections merely turning on the swivel joints 16.This procedure for removing the tube-grates from the tank may be used incase of necessity for repairing or renewing the lair-tubes 1,6 obviatingany necessity for emptying the apparatus,and reducing the effects of theinterruption to the continuity of its operation to a minimum. Inrestarting after a considerable period of delay with the tank full ofpul the arms 9 should be lowered until the c ains 12 are slack, thevertical shaft 4 should be caused to rotate, and air turned on throughthe pipe 13. When the arms 9 have worked their way down to their normalposition, the tube-grates.should be lowered into their position, whenthe air may be turned into them, the feed to the apparatus turned on,and normal operation resumed. As an alternative to the use of anair-lift for elevating the pulp in the hollow conduit, mechanical meansmay be used if desired, such as a boat propeller, or Archimedean screwor other. device not wastin power in violent agitation of the pulp. nFig. 7 of the drawing I show an Archimedean screw, 35, within casing,2*, for elevating the pulp. The shaft, 33 of the screw extends upwardlythrough a sleeve, 4*, held in supports, 5, the sleeve, 4, carrylatterbeing mounted on ing the plup distributor and scraper, 7" and 10. hescrew is driven by the bevel gears 36 and the sleeve by the bevel gears(3, the the shaft of the spur gear 38 which meshes with spur gear 37 onthe shaft of one of the bevels 36. The lower end of the screw shaft ismounted on a step-bearing, 34, in connection with which means may beprovided as illustrated for supplying water under pressure forlubrication.

It is to be understood that other forms of tube-grate may be used,differing from that particularly described herein, all that is necessarybeing some device for emitting fine airbubbles, uniformly distributed,and through which the pulp can pass in its path of circulation althoughI consider the specific construction of the tube-grate illustrated anddescribed as novel and advantageous.

The apparatus disclosed is not claimed herein but forms the subjectmatter of a divisional application filed December 21, 1920, Ser. No.432,291. 1

I claim:

' 1. In a flotation process the operations of maintaining throughout theentire horizontal cross-sectional area of a body of freelyflowing orepulp a substantially uniform ascendmg co umn of minute gaseous bubbles,maintaining throughout said area a substantially homogeneous descendingcolumn of pulp, elevating pulp from the lower part of said body of pulpand dischargingv it substantially uniformly throughout the horizontalcross-sectional area of the upper part of said body of pulp therebycausing circulation of said pulp 1n a homogeneous column, and separatingthe floated mineral from the remainder of the ulp 2. In a flotationprocess tlie operations of maintaining throughout the entire horizontalcross-sectional area of a body of freelyflowing ore pulp a substantiallyuniform ascending column of minute gaseous bubbles, maintainingthroughout said area a substantially homogeneous descending column ofpulp, elevating pulp from the lower part of said body of pulp anddischarging. 1t substantially uniformly throughout the horizontalcross-sectional area of the upper part of said body ofpulp therebycausing circulation of said pulp in a homogeneous column, keeping thepart of said body of pulp through "which said bubbles rise free frommovement other than the ascent of the bubbles and descent of the pulpcolumn, and separating the floated mineral from the remainder of thepulp.

3. In a flotation process the operations of maintaining throughout theentire horizontal cross-sectional area of a bod of freelyfiowin ore pulpa substantial y uniform ascen ing coumn of minute gaseous bubbles,maintainin throughout said area a substantially homogeneous descendingcolumn of pulp, pneumatically elevating pulp from the lower part of saidbody of pulp and dischargingit substantially uniformly throughout thehorizontal cross-sectional area of the upper part of said bod of pulpthereby causing circulation of sai pulp in a homogeneous column, andseparating the floated mineral. from the remalnder of the pulp.

4. In a flotation process the operations of maintaining throughout-theentire horizontal cross-sectional area of a body of'freelyflowing ore1pulp a substantially uniform ascending co umn of minute gaseousbubbles, maintaining throughout said area a substantially homogeneousdescending column of pulp, pneumatically elevating pulp from the lowerpart of said body 0 pulp and discharging it substantially uniformlythroughout the horizontal cross-sectional area of the upper part of saidbod of pulp thereby causing circulation of sai pulp in a homo-geneouscolumn, the part of said body of pulp through which'said bubbles risebeing kept free from movement other than that due to the ascent of thebubbles and descent of the pulp column, and separating the floatedmineral, from the remainder of the pulp.

5. In a flotation process the operations of maintaining throughout theentire horizontal cross-sectional area of a body'of freelyflowing orepulp a substantially uniform ascending column of minute gaseous bubbles,maintaining throughout said area a substantially. homogeneous descendingcolumn of pulp, permitting said ulp column to descend to a'level belowsaid ascending column of bubbles, elevating pulp from below said columnof bubbles and discharging it substantially uniformly throughout thehorizontal cross-sectional area of the part of the body of pulptraversedby said column of bubbles thereby causing circulation of saidpulp in a homogeneous column, and separating the floated mineral fromthe remainder of the pulp.

6. In a flotation process the operations of maintaining 'throughout theentire horizontalcross-sectional area of a body of freelyflowing orepulp a substantially uniform ascending column of minute gaseous bubbles,maintaining throughout said area a substantially homogeneous descendingcolumn of pulp, permittin said ulp column to descend to a level be owsaid ascending column of bubbles, elevating pul from below said columnof bubbles and i'scharging it substantially uniformly throu bout thehorizontal cross-sectional area of t e part of the body of ulp traversedby said column of bubbles t ereby causing circulation of said pulp in ahomogeneous column, the part of said pulp through which said bubblesrise being kept free from movement other than that due to the ascent ofthe bubbles and descent of the pulp column, and separating the floatedmineral from the remainder of the pulp.

7 In a flotation process the o erations of to descend" to a level belowsaidascending column of bubbles, pneumatically elevatfrom below saidcolumn of bubing pul discharging it substantially unibles an formlythrou hout the horizontal cross-secs tional area 0 the part of the bodyof pulp traversed by said column ofbubbIes thereby causing circulationof said pulp in a homo-.

g neous column, and separating the floated mineral from the remainder ofthe pulp.

' 8.- In a flotation process the operations of maintaining throughoutthe entire horizontal cross-sectional area of a body of freely flowingore pulp a substantially uniform ascending column of minute gaseousbubbles, maintaining throughout said area a substantially homogeneousdescending column of pulp, permitting said pulp column to descend to alevel below said ascending column of bubbles, pneumatically elevatingpulp from below said column of bubbles and discharging it substantiallyuniformly throughout vthe horizontal cross-sectional area of the part ofthe body of pulp traversed by said column of bubbles thereby causingcirculation of said pulp in a homogeneous column, the part of said bodyof pulp through which said bubbles rise being kept free from movementother than that due to the ascent of the bubbles and descent of thepulp'column, and separatin the floated mineral from the remainder o? thepulp. 9. Ina flotation process the operations of maintaining throughoutthe entlre horizontal cross-sectional area of a body of freelyflowin orepulp a substantially uniform ascending column of minute gaseous bubblesintroduced through the pores of a permeable medium, maintainingthroughout said area a substantially homogeneous descending column ofpulp, permittingsaid pulp column to descend through substantiallyuniforml distributed spaces between parts of sai permeable medium,elevating pulp from beneath said permeable medium and discharging itaboye said medium substantially uniformly throu bout the horizontalcross-sectional area'o the part of the body of pulp traversed by saidcolumn of bubbles thereby causing circulation of said pulp in ahomogeneous column, and separating the floated mineral from theremainder of the pulp.

10. Ina flotation process the operations of maintaining throughouttheentire horizontal cross-sectional area of a body of freelyflowing orepulp a substantially uniform ascending column of minute gaseous bubblesintroduced through the pores of a permeable medium, maintainingthroughout said area a substantially homogeneous descending column ofpulp, permitting said pulp column to descend through substantiallyuniformly distributed spaces between parts of said permeable medium,elevating pulp from beneath said permeable medium and discharging it'above said medium substantially uniformly throughout the horizontalcross-sectional area of the part of the body of pulp traversed by saidcolumn of bubbles thereby causing circulation of said pulp in ahomogeneous column, the part of said body of pulp through which saidbubbles rise being kept free from movement other than that due to theascent of the bubbles and descent of the pulp column, and separating thefloated mineral from the remainder of the )ulp. l 11. In a flotationprocess the operations of maintaining throughout the entire horizontalcross-sectional area of a body of freely flowing ore pulp asubstantially uniform ascending column of minute gaseous bubblesintroduced through the pores of a permeable medium, maintainingthroughout said area a substantially homogeneous descending column ofpulp, permitting said pulp column to descend through substantiallyuniformly distributed spaces between parts of said permeable medium,pneumatically elevating pulp from beneath said permeable medium anddischarging it above saidmedium substantially uniformly throughout thehorizontal cross-sectional area of thepart of the body of pulptransversed by said column of,

, bubbles thereby causing circulation of said pulp in a homogeneouscolumn, and separating the floated mineral from the remainder of thepulp.

12. In a flotation process the operations of maintaining throughout theentire horizontal cross-sectional area of a body of freelyflowing orepulp a substantially uniform,

ascending column of minute gaseous bubbles introduced through the poresof a permeable medium, maintaining throughout said area a substantiallyhomogeneous descending column of pulp, permitting said pulp column todescend through substantially uniformly distributed spaces between partsof said permeable medium, pneumatically elevating pulp from beneath saidpermeable medium and discharging it above said medium substantiallyuniformly throughout the horizontal cross-sectional area of the part ofthe body. of pulp traversed bysaid column of bubbles thereby causingclrculation of said pulp in a homogeneous column, the part of said bodyof pulp through which said bubbles rise being kept free from movementother than that due to the ascent of the bubbles and descent of the pulpcolumn, and separating the floated mineral from the remainder of thenip.

13. A process or the concentration of ores and the like by frothflotation, whichcomprises maintaining a body ofore-pulp, in-

troducing fine air bubbles initially too small to effect any substantialagitation into the pulp above the bottom thereof, collectlngthe frothformed above said pulp, and effecting circulation of the 'pulp withoutviolent agitation by withdrawing'pulp from below the zone of airintroduction, elevating the Withdrawn pulp, and discharging the elevatedpulp into the body of ore pulp below the sur throughout the horizontalsectional area of said body of pulp. v

In tes'tlmon whereof I aflix m si ature.

ALLET RICE R B INS.

ace thereof and substantially uniformly

